The present invention relates to a method of automatically setting optimal model parameters in a fuel transport delay compensation method using a dynamic model.
The conventional methods of compensating for a delay in fuel transport by use of a dynamic model includes methods disclosed by Japanese Patent Application un-examined laid-open No. JP-A-58-8238 and U.S. Pat. No. 4,939,658. In these methods, the characteristics including the rate of adhesion, the rate of evaporation and the rate of parameters are beforehand formulated through predetermined experiments and the quantity of fuel injection is determined by use of those characteristics. For the formulation is used a method which is disclosed by, for example, Proceedings of the Scientific Lecture Meeting of Japan Automobile Technology Association, 842049. In the disclosed method, the formulation of characteristics is made by determining parameters so that a measured response of an air/fuel ratio of an exhaust gas, when the fuel injection quantity is stepwise changed in a state in which various conditions of an engine are constant, coincides with that response which is calculated using a fuel transport model.
The above prior art involves a problem that a desired control performance cannot be obtained even if the characteristics inclusive of the adhesion rate, the evaporation rate and the runaway rate determined by the predetermined experiments are set to a fuel control system as they are.
Also, in the above formulation method, it is not possible to uniquely determine the parameters since the measured response of the air/fuel ratio of the exhaust gas has a large variation even under the same engine operating condition. Therefore, a method may be considered in which the average values of parameter determined from several kinds of measured response is produced for use as a real parameter value for a certain operating condition. However, even by use of this method, there is a large possibility that the determined parameter includes an error. Therefore, even if the determined parameter is set to the control system as it is, a desired control performance cannot be obtained. Accordingly, the matching (or tuning) of a fuel system parameter becomes necessary.
Further, even if the parameter can be determined with satisfactory accuracy, there is the following problem concerning the detection of an air quantity. In order to obtain a desired performance of air/fuel ratio control, the quantity of air used for calculating the fuel injection quantity must be the quantity of air which flows into a cylinder. At present, an Hot Wire sensor or a pressure sensor is used for the detection of the air quantity. However, due to a delay in response of the sensor, the arrangement of the sensor, a processing for smoothing of pulsation or ripple, and so-on, it does not always follow that the detected air quantity coincides with the quantity of air which flows into the cylinder. This error in air quantity causes an air/fuel ratio control error. The matching of a fuel system parameter becomes necessary for making compensation for the air/fuel ratio control error.
As mentioned above, the matching of a fuel system parameter must be taken in order to obtain a desired control performance. In the existing circumstances, the matching is taken through the operation of an actual engine or an actual motor vehicle by a person. There is a problem that the matching must be taken in various operating ranges and hence a considerable number of steps are required for the development of a system.
Further, in the prior art, no consideration is made for a temporal change of the fuel transportation characteristic in an intake manifold. Accordingly, there is a possibility that the air/fuel ratio control performance is deteriorated with an increase in number of times of operation of an engine.